I've seen this face before

We have known for some time that there is a network of brain regions for face recognition. However, how and where face familiarity is encoded has been elusive for decades. Landi and Freiwald performed brain imaging in macaques and identified two areas specifically involved in recognizing familiar faces. These two areas showed a nonlinear response as blurred faces gradually became visible, rapidly becoming active when the faces of familiar monkeys became recognizable.

Abstract

Familiarity alters face recognition: Familiar faces are recognized more accurately than unfamiliar ones and under difficult viewing conditions when unfamiliar face recognition fails. The neural basis for this fundamental difference remains unknown. Using whole-brain functional magnetic resonance imaging, we found that personally familiar faces engage the macaque face-processing network more than unfamiliar faces. Familiar faces also recruited two hitherto unknown face areas at anatomically conserved locations within the perirhinal cortex and the temporal pole. These two areas, but not the core face-processing network, responded to familiar faces emerging from a blur with a characteristic nonlinear surge, akin to the abruptness of familiar face recognition. In contrast, responses to unfamiliar faces and objects remained linear. Thus, two temporal lobe areas extend the core face-processing network into a familiar face-recognition system.